1. Field of the Invention
The present invention relates to a saddle riding type vehicle such as a three-wheeled or four-wheeled automotive vehicle having a pair of wheels at least at a rear portion of a vehicle body, which can make turns by leaning the vehicle body.
2. Description of the Related Art
Conventionally, this type of vehicle includes a saddle riding type vehicle having two rear driven wheels, which can make turns by leaning a vehicle body. With such a vehicle, it is common practice to drive the two rear wheels with chains instead of driving only one of the rear wheels.
Chains have a characteristic to become elongated through use. In order to assure proper drive, it is necessary to adjust tension of the chains by adjusting positions of the rear wheels. Although the chains of the two rear wheels are adjusted, the two chains usually are different in the degree of elongation. Therefore, when tension of the chains is appropriately adjusted for the two rear wheels, there arises a problem of creating different wheelbases which are the distances between the two rear wheels and front wheel(s).
There exists a three-wheeled vehicle employing a shaft drive in place of the chain drive in order to eliminate the above inconvenience associated with maintenance (see Japanese Unexamined Patent Publication S61-125973 (FIG. 13), for example). This three-wheeled vehicle has front bevel gears provided for a drive shaft of a differential mechanism to transmit output from an engine output shaft in perpendicular directions, and a shaft disposed rearward of each bevel gear to transmit the drive. A rear bevel gear is disposed at the rear end of the shaft to transmit the drive to each rear wheel, thereby to rotate the rear wheels based on the drive. The two rear wheels are rotatably supported by a single rear fork, and each shaft has a universal joint disposed further rearward than a pivot axis of the rear fork.
However, the conventional example with such a construction has the following drawbacks.
The conventional vehicle, with the shaft drive mechanism, can eliminate the inconvenience associated with maintenance. However, because of the positional relationship between the rear fork and universal joint, when the rear end of the rear fork moves very close to the vehicle body, more particularly, when the vehicle body sinks greatly relative to the rear fork or the rear fork flips up relative to the vehicle body, there arises a problem that the engine output cannot be transmitted to the rear wheels efficiently.
In the conventional construction, because the two rear wheels are attached to the single fork, the vehicle body and rear wheels never lean relative to the vertical direction, and thus the rear end of the rear fork rarely moves very close to the vehicle body. However, with a vehicle of the type in which each of the two rear wheels has a single rear fork, and the two rear wheels lean with the vehicle body from the vertical direction, the rear fork of the rear wheel located inward, when in a leaning position, moves very close to the vehicle body with increased frequency. When the technique of the conventional example is applied to that case, the efficiency of transmission will be significantly decreased.